1. Field of the Invention
This invention relates to lightweight, portable, vibrating concrete screeds and more specifically to air-operated vibrating screeds.
2. Description of the Prior Art
Lightweight, portable, vibrating, concrete screeds of the type to which the present invention is generally related are described in applicant's prior U.S. Pat. No. 4,030,873 and the referred to copending applications Ser. Nos. 883,955 and 29,654. The general state of the art is believed to be fully set forth in these references and therefore will not be restated except for pointing out certain prior art practices which specifically relate to the subject matter of the present invention.
In particular, since the present invention is directed to an air-powered concrete screed, it should be noted that air vibrators have been secured to both leading and trailing screed blades in a staggered relationship as a means of vibrating the elongated screed frame. However, this arrangement means that each point of vibration requires its own air vibrator. Also, this arrangement does not allow the vibrations from each air vibrator to be imparted to both leading and trailing blades. Thus, it would be desirable to provide an air-vibrated concrete screed in which a lesser number of air vibrators were required to achieve the vibration. Also, it would be desirable to provide an arrangement by which each vibrator could establish points of vibration offset from each other lengthwise of the screed frame.
As another aspect of the type of construction used in portable vibrating concrete screeds of the type to which the invention relates, it may be noted that the typical screed frame is made up of components which are welded together. Due to the stringent operating requirements and heavy wear encountered on the job, it is not uncommon for a frame member to be bent or damaged and thus require replacement. An all-welded construction, of course, makes replacement of an individual frame component both time consuming and expensive. Since the typical portable, concrete screed of the type to which the invention relates has a triangular cross section, it has become the practice to use a piece of ordinary steel pipe running lengthwise of the frame at the apex of the triangle and the frame braces are welded to this pipe. This pipe has also been used as a conduit for carrying pressurized air and air vibrator hoses have been connected to the pipe as a means for supplying air to the vibrators. While the use of a pipe member of this type as both a structural member and as an air conduit is advantageous, a simple round pipe of this kind does not lend itself readily to the type of screed frame in which the members are bolted together for ease of replacement when damaged. Thus, there is a need for an improved screed frame adapted to be bolted together and employing an improved apex tube construction that both lends itself to serving as an air conduit as well as a structural member which can be easily bolted to other structural members for establishing a relatively rigid screed frame.
As a further aspect of screed constructions, it has been known to provide means enabling one screed section to be angled relative to another screed section to adjust to concrete pouring operations where a crown or valley shape is formed with the screed. Thus, with air-operated screeds, it would be desirable to provide an air-operated screed frame construction in which a tubular member located at the apex of the triangular-shaped frame and serving as an air conduit could also be used as a means for adjusting one screed section relative to another. However, such an arrangement has not been previously known in prior art screed frame constructions.
The use of winching mechanism on portable vibrating concrete screeds of the type to which the invention relates has been well established. However, so far as applicant is aware, it has not been heretofore known to provide an air-operated winch in conjunction with an air-operated screed and arranged such that air can be supplied both to the winch mechanism as well as to the air vibrators through a common structural member.
The object of the invention thus becomes that of providing an improved air screed aimed at overcoming the shortcomings of prior screed constructions as discussed above. Other objects will become apparent as the description proceeds.